Symbiosis
by Jordanna Morgan
Summary: Kurusu gives Ikoma a new perspective on his role aboard the Kotetsujo.


**Title:** Symbiosis  
 **Author:** Jordanna Morgan  
 **Archive Rights:** Please request the author's consent.  
 **Rating/Warnings:** G.  
 **Characters:** Ikoma and Kurusu.  
 **Setting:** Sometime after episode four.  
 **Summary:** Kurusu gives Ikoma a new perspective on his role aboard the _Kotetsujo_.  
 **Disclaimer:** They belong to Kabaneri Committee and other relevant parties. I'm just playing with them.  
 **Notes:** So, there's a new fandom in my life. I fell ragingly in love with "Kabaneri of the Iron Fortress" on my first binge-watch… which I'd say was pretty inevitable, for reasons that may be obvious to anyone who knows the patterns of my fandoms. _*g*_ And of course little iron-hearted bunnies started hopping quickly, because this started the next day. The result is my first fic in the fandom—and it definitely won't be the last.

* * *

Ikoma threaded his way from the rear car of the _Kotetsujo_ in a slow limp, wincing as he gingerly stretched and flexed his muscles. Kabaneri healing capacity be hanged: his entire body felt like one big bruise, and the many gashes and abrasions glaring out from his sallow skin had only recently stopped bleeding.

Such was the distressingly familiar aftermath of another day of combat training with Mumei.

He didn't really blame her. In her own gleefully berserker way, he knew his fellow Kabaneri was only trying to help him become stronger. The real root of the problem was that… well, his brain just couldn't convince his fists _not_ to pull their punches against the girl. Not even when he knew she was an inhumanly tough little terror, and she was going to wipe the deck with him yet again if he gave her an ounce less than he got.

It probably had something to do with thoughts of his sister. Most things seemed to these days, anyhow—and _especially_ when Mumei was around.

As it was early evening, many of the train's passengers were tucking into their dinner rations. A few women still discreetly shrank back as Ikoma passed through, and a few men glowered at him suspiciously from beneath their brows; but more often he received smiles and politely murmured greetings. He was glad for that trust he had fought so hard to gain. Even locked within a Kabane's iron cage, his heart contained only the desire to protect these people.

One young girl dropped her gaze when he came near, furtively slipping her food behind her back. There was only the smallest hesitation in his step as he read and understood those guilty movements. He realized the child felt bad to let him see her eating, because she knew the Kabaneri could no longer partake of normal food himself.

For the first time Ikoma permitted himself to give that matter deliberate thought. Up to this point, he had been preoccupied with more immediate problems like saving his skin from Kabane and humans alike, and reconciling his mind to the abhorrent new nourishment his body _did_ crave. Now that he considered it, the aroma of food that hung thickly in the air held no appeal for him. For a moment he toyed abstractedly with the idea of envying those around him—the people who could still eat green growing things, enjoying all their rich and varied flavors—but any spark of bitterness was dulled by the sheer disinterest of his stomach. Food simply wasn't _food_ to him anymore, and he felt nothing about it at all.

Had it been blood that he smelled instead, it would have been a very different story.

Ikoma grimaced and quickened his step. At the moment his own resting place was in a smaller compartment ahead, which he shared with an unlikely contrast of bunkmates. On the one hand were Takumi and Sukari, fellow steamsmiths who still saw in him the person they had known when he was human. On the other were Kurusu and Kibito: brave bushi who had never really known him as anything but the creature he was now, yet chose to accept his presence anyway.

…At least conditionally. Since the day Miss Ayame gave him permission to roam the train freely, Ikoma knew very well that Kurusu, at the least, had taken up quarters in the same compartment to watch him. He didn't begrudge that at all, because they both wanted the same thing. They wanted everyone aboard the _Kotetsujo_ to be safe—even if it came to keeping them safe from Ikoma himself.

Kurusu hadn't slept much for some time then; but lately, peering through the dark with inhumanly perceptive new eyes, Ikoma saw much more often that the warrior's face had relaxed into unguarded slumber. That in itself was a show of trust that made his heart thump against its metal confines.

Slipping through the hatch, Ikoma found the compartment deserted save for Kurusu himself, who was seated on his bunk with sword and polishing cloth in hand.

Not very long ago, Kurusu would have reacted to Ikoma's appearance by pointing that blade at him and snarling threats. Now he simply regarded the Kabaneri with cool appraisal, laying the sword down at his side. His expression was matched by the politely impersonal tone of his greeting. "Good evening."

"…Hey." Ikoma pulled the hatch closed and shed his tattered crimson cloak, needlessly glancing around the compartment. "Where is everybody?"

"That girl Kajika dragged your steamsmith friends off somewhere. Kibito is on watch. I'm only here to rest for a while, before I take the place of a sick man on the overnight shift." Kurusu's gaze flickered across Ikoma's upper body, cataloguing purple and scarlet blotches that further enlivened the pale red-veined skin between straps of metal and leather. "And on that note, you don't look particularly healthy yourself."

Ikoma smiled wanly and tilted his hand in lieu of a shrug, because moving his shoulders would have ached too much. "No, I'm good. Mumei was just a little more… _playful_ than usual today."

"Or maybe you weren't at your best form. Those sparring wounds she leaves on you have usually faded more than that by the time you come back here." The bushi narrowed his too-observant eyes. "How long has it been since you last had blood?"

That question caught Ikoma up short.

"Uh—yesterday evening?" He frowned. "No. Actually, it was yesterday _morning_."

Over thirty-six hours, then. Oops. Perhaps that really did explain why his body wasn't quite up to speed that day.

"But surely you've become hungry by this time," Kurusu muttered darkly.

"Well… yeah, a little. I mean, not as much as if I'd had to do any _real_ fighting. But I don't like asking for blood any sooner than I need to, and—I guess I just lost track."

"That's no good, Ikoma. You need to mind yourself more carefully than that—for _all_ our sakes." Kurusu's right hand wandered to the leather vambrace on his left arm, beginning to tug loose its lacings. "It's dangerous to stretch the time between your feedings too far."

In some gapingly incredulous part of his mind, Ikoma divined the intent of Kurusu's casual movements. The realization gave him a subtle flash of panic.

"No, I'm fine, really! I'll just go and—"

The protest was cut short by a flash of steel, as Kurusu's sword traced a shallow gash across the bared flesh of his own inner forearm. He laid the weapon aside and extended his arm, showing the drops of red that began to well up.

"Take it," he said simply.

Ikoma felt his face grow hot. He tore his gaze away from the cut and shook his head, wrapping his arms around the strangely contrasting chill in his insides.

"No, I… I won't do it that way." His voice was faint. He swallowed, but his next words only came out more weakly. "…Not again."

Kurusu uttered a noise of perplexity. For an instant Ikoma met the wide eyes that stared back at him; but then it was Kurusu's gaze that shifted away, quickly scanning the cramped space of the compartment. Seeing a metal cup that protruded from the top of a rucksack, he snatched it up and positioned it under his arm. Only by a heartbeat did he spare the sheets of his bunk from being stained by the first drip of blood.

"For a creature who can only survive on one food, you're starting to get damned _picky_ ," he muttered archly.

"Sorry. It's just that I can't stand the thought of… of putting my _mouth_ on someone to drink it again. It's too much like…" Ikoma gulped. "Like _them_."

…And there was _that_ fear, even still. Now that he was being fed regular rations of blood, he felt as close to normal as he ever had since he became a Kabaneri: no pains, no staggering weak spells, no lapses of his mind into a terrifying darkness. But what if something should happen to disrupt that fragile stability? If he was trapped somewhere, if he was separated from his chain of sustenance aboard the _Kotetsujo_ …

Willfully he shook off that thought, only to realize the silence that met his words felt decidedly… _heavy_. He looked up to see Kurusu studying him with a grim, thoughtful gaze. All the while, blood continued to slide down the bushi's wrist and into the cup.

"You're never going to become one of them, Ikoma." His deep voice was firm and steady. "Because if I ever see it happening to you… you won't live a moment longer than that."

The words were like many things Kurusu had said before, but the meaning was not the same at all. Back then they had been threats; but this time, it was a _promise_. Kurusu knew that Ikoma understood the difference.

Slowly Ikoma took in a deep breath, letting his hands fall to his sides. His voice carried only the weight of sincerity when he whispered, "Thanks, Kurusu."

No reply was offered, and none was needed. Silence stretched between them for a short interval. Ikoma could smell Kurusu's blood, awakening the unnerving dark flutterings of the appetite he now possessed, but he shoved those sensations to the back of his awareness. They would be quieted soon enough.

"Were you _testing_ me by cutting your arm like that?" he asked at length.

" _No_ ," Kurusu retorted. He seemed oddly affronted by the suggestion—but his scowl faded swiftly when he glanced down at his self-inflicted wound. "This world tests all of us enough."

The last words were nearly inaudible, murmured like a stray inner thought. Then he blinked as if waking from a reverie, and focused on Ikoma once more. "I only meant to make sure your _mistake_ was promptly corrected. You weaken when you've gone too long without blood. …When we could run into danger at any time, a weapon should always be kept primed to its full strength."

"Is that what you've decided I am?"

There was no trace of resentment or dismay in the inquiry. Ikoma merely wanted to know.

"It's what you've chosen to be yourself." Kurusu's eyes were hidden beneath his hair, his attention focused suddenly and intently on his arm. He made a fist and tensed his muscles, urging a final few drops out of the slowing trickle of blood. "I don't think you disagree with that."

Ikoma let out his breath in a hollow half-laugh. "You're right."

Another silence fell. When the bleeding had stopped, Kurusu rather carelessly knotted his polishing cloth around his arm. Then his right hand swept up the cup with its scarlet contents, and he held it out to the Kabaneri.

Feeling a bit ridiculous, Ikoma stepped forward and accepted the offering. He stared into it meditatively for a moment, trying in his mind to disassociate the red liquid from the living person he had just watched it flow out of. The effort failed, but he knew it would be best to simply get the rotten business over with anyway.

With some reluctance, he began to raise the cup to his lips; but he was suddenly conscious of the fact that Kurusu's gaze still rested on him. The realization made him freeze. He was used to drinking blood together with Mumei, but in front of a human… And especially the very human whose veins had just _provided_ the blood…

"Don't _look_!" he objected sharply, clutching the cup to his chest with an absurd sort of possessiveness.

A familiar flush of innate obstinacy crept over Kurusu's face. "It is _my_ blood, idiot. I think I have the right to watch you drink it."

With a frustrated huff, Ikoma gave up the idea of arguing. He turned his back and gulped the blood down quickly.

It was still warm—and much more distinct in its flavor than the usual prepared rations he and Mumei received, which were not nearly so fresh. Newly-spilled, Kurusu's blood was not sweet steel like Miss Ayame's, but instead filled with a surprisingly deep and mellow richness. It flowed through Ikoma like a calming wave, silencing his hunger, easing his aches.

The Kabaneri loathed himself for the sated and comfortable pleasure his body made his mind feel then.

His thin frame would not have shielded much of the sight from Kurusu, he knew. He breathed deeply, swiped his hand across his mouth, and finally turned to face the provider of the meal. The warrior looked back at him, pensive yet alert, with no sign of revulsion or blame on his face… and somehow, that only made Ikoma feel worse.

A dull _clang_ resounded through the compartment. The cup hit the wall hard enough to acquire a dent, spattering a few crimson drops on the deck plates as it fell.

"I _hate_ this!"

Kurusu said nothing. Ikoma clenched his fists to still his sudden shaking.

"I hate being a slave to the need of this corrupted body. I hate knowing that others have to _suffer_ just to let me survive. I hate living like a… a _parasite_ on the people I only want to _protect_!"

For a few moments, his heavy breaths were the only sound to be heard over the dim squeal and rumble of the train's wheels beneath them.

And then Kurusu spoke.

"If you're finished feeling sorry for yourself, I want to ask you a question."

Struck by the words like a slap in the face, Ikoma jerked his head up to stare at Kurusu in astonishment. Mumei had flung the same accusation at him before, at the drawbridge of Aragane Station—after he tried to be left behind so that no one would be hurt by whatever it was he had become. When he was only thinking about the good of others, that conclusion they had both somehow come to made no sense to him at all.

" _What_? How is it feeling sorry for _myself_ to—"

"Do you know how many people have offered their blood for you and Mumei?"

Startled into momentary silence by the question, Ikoma blinked. His anger was forgotten as a number stood out in his mind, bringing with it the renewed whispers of a more sullen guilt.

"After Miss Ayame told us we could stay… I think Takumi said there were eight of you who volunteered." He grimaced at the thought that two Kabaneri should be placing such a burden on four times that number of humans.

"That was the start," Kurusu acknowledged quietly. "But we were only the first. As of now, more than forty people have come forward to provide for you. Steamsmiths, bushi, Aragane townspeople—and every one of them a willing donor."

The abrupt thud of Ikoma's heart felt as if it might burst its cage.

 _More than forty…_

He hadn't known. He never even would have imagined the possibility.

"… _Why_?" he breathed incredulously. "Why would that many people want to spill their blood to help _us_ stay alive?"

Slowly and gracefully, Kurusu rose from his bunk to face the smaller young man. His eyes were hard, but every bit of unkindness they had ever held was now absent from those indigo depths.

"Listen to me. Since the day Miss Ayame chose to keep you with us, the passengers have learned about the improvements you've made to our weapons. Some of them have also seen you and Mumei in battle firsthand." His voice became a shade softer. "Many of those who are giving you their blood could only dream of being able to fight the Kabane at all, much less in the ways you can. They don't have the strength for that in themselves. But they do have another kind of strength they can offer to you Kabaneri—so that you can fight _for_ them."

Something closed around Ikoma's throat more tightly than the restraining collar he wore. A sudden warmth burned in his eyes. He caught his breath and took a step back, sinking down onto the edge of his bunk.

The way Kurusu was describing the relationship between the Kabaneri and the passengers of the _Kotetsujo_ …

It wasn't parasitic. It was symbiotic: the cooperation of two disparate life forms to gain a mutual benefit. In this case, it meant nourishment in exchange for protection. It was an elemental pattern, designed by nature itself.

" _Symbiosis_ … Could that really be what's happened here?"

Kurusu may or may not have heard that unrealized whisper. Regardless, he paid it no heed. An intrusive rustle of blue caused Ikoma to blink his vision into focus, and he found himself staring into the eyes of the bushi who crouched before him like a panther. Although the intent was different, his gaze was as deadly serious as it had been when he pulled the trigger of a steam rifle pointed at Ikoma's chest.

"Make no mistake. In return for our sustaining your lives, your obligation is to put those lives on the line. Our people expect you to use every advantage of those blood-fueled bodies of yours to fight the Kabane—face to face. To suffer being bitten and torn by those monsters. To relive again and again the very wounds that made you what you are." Kurusu released a heavy breath. "You see, our part of the bargain may come at a high price, _Kabaneri_ … but so does yours. So don't hesitate to ask for all you need. I can assure you, it will be required back from you in full measure."

…And just that easily, something fell into place that Ikoma hadn't known he so badly needed.

 _People_ can _help being afraid_ , he had once insisted to Mumei—and now the very validation of that belief was what kept him alive, because those who opened their veins for him had _chosen_ not to fear him any longer. On the contrary, they had decided his presence was worth his wages of blood. All they asked in return was that he keep doing for them the things he knew he could do; and in his ironbound heart, there had never been a greater wish than exactly that.

He was wanted after all.

Tears brimmed behind his glasses, but they were dashed an instant later by bright, exultant laughter. Ikoma threw his head back and let himself revel in that giddiness of relief. The weight of the insidious metal cage within his chest felt suddenly much lighter.

Kurusu promptly shied away from Ikoma's hysterics, looking baffled and somewhat irritated. Laughter was clearly the _last_ reaction he might have expected his grave words to be met with.

"You really _are_ crazy," he murmured, but his tone belied the brusqueness of the words. It was merely a sigh of bemused resignation: the hapless auditory shrug of a man so worn down by the impossible that he didn't have the will to question it anymore.

Ikoma hiccupped and sniffled, swallowing the last of his chortles. And then… then, he had the impertinence to reach out and rest his hands on the bushi's broad shoulders, giving them a quick grateful squeeze.

"No." He smiled warmly at Kurusu. "I just finally figured something out, that's all."

A shadow of skepticism passed through Kurusu's eyes. He shook his head in exasperated dismissal—and then his own hand came out of nowhere to give the side of Ikoma's head an ungentle push, shoving him down flat onto his bunk as effectively as a judo throw.

"Fine." He rose and turned away, adjusting the makeshift wrapping on his arm. "Then go to sleep or go somewhere else. I have a watch to stand in three hours."

The Kabaneri grinned, finding his cloak with one hand to pull it over himself like a blanket. "Yeah. I guess I _could_ use a rest."

"No doubt." The compartment's light was extinguished. In the scant remaining moonglow, Kurusu's dark figure retreated to his own bunk. "You always look half-dead, but tonight you look three-quarters dead."

"…One more crack like that, and just maybe I _will_ bite next time," Ikoma grumbled into his pillow.

It said much that only a faint, flat chuckle drifted back across the narrow space.

Left in silent darkness, Ikoma rolled over and draped his arm across his eyes, allowing Kurusu's revelations to settle within his mind. He had believed only those most familiar with himself and Mumei were willing to bleed for them, but now… Of all those people who smiled at him as he passed through the train, having become appreciative of the _Kotetsujo_ 's Kabaneri defenders, how many had taken the further step of offering blood to support them? Evidently more than he had imagined ever would. Yet he wouldn't try to guess at which ones they were, because it was probably better that way. Not knowing, he would simply want to fight harder for _all_ of them.

He decided then that whatever draconian training exercises Mumei inflicted on him the next day, he was finally going to _beat_ her at them. He would become skilled like her, learning how best to use the strength provided to him by the people he protected in turn. He would give them all even more than he received.

If this was really symbiosis, it was a kind that nature could never have intended, but he would make it work—because after all, he wasn't _just_ a Kabaneri. The fact tended to be obscured by his more incredible aspects these days, but he was still a steamsmith too.

And as everyone knew, a good steamsmith could make _anything_ work.

* * *

 _2018 Jordanna Morgan_


End file.
